I. Field of the Invention
The present invention relates generally to cryogenic storage devices and, more particularly, to a cryogenic tank adapted to receive biological specimens.
II. Description of the Prior Art
There are many previously known cryogenic storage tanks which are generally cylindrical in shape and have a closed bottom and open top thus defining a cryogenic freezing chamber. A source of liquefied gaseous material, typically liquid nitrogen, is fluidly connected to the interior of the chamber through a valve system so that the liquid level with the cryogenic chamber is maintained within predetermined limits. A lid is also conventionally disposed across the open top of the cryogenic tank.
In use, frozen biological specimens, such as blood, semen or other types of biological specimens, are simply immersed in the liquid contained within the cryogenic chamber thus storing the biological materials in the desired fashion. Since the temperature of the liquefied gaseous material is extremely low, e.g. below -191.degree. C., the viability of the biological specimens can be maintained for long periods of time.
One disadvantage of these previously known cryogenic storage devices, however, is that, since the biological specimens are immersed within the liquefied gaseous material, cross contamination between the biological specimens is possible. For example, in the event that a biological specimen leaks into the liquefied gaseous material, any impurities, diseases, viruses or the like contained within that biological specimen may thereafter be transmitted to a different biological specimen also contained within the cryogenic freezing tank by using the liquefied gaseous material within the tank as the transportation mechanism for such undesirable contaminants.